Effect Of Wollastonite On Properties Of Engineered Cementitious Composites

Engineered cementitious composites(ECC)has higher mechanical strength,durability and engineering value than ordinary concrete,more and more scholars began to study of such materials.However,the large composition of binding materials in ECC will not only bring problems of large shrinkage deformation and high hydration heat,but also cause environmental pollution due to the massive use of cement.Wollastonite is a microscopic mineral material with needle-like and fibrous crystal forms,which can be used in concrete materials to improve its mechanical properties and durability.There are relatively few studies on the effect of wollastonite on the properties of ECC materials.In order to verify the feasibility of adding wollastonite into ECC,this paper conducted experimental studies from the aspects of workability,mechanical properties,shrinkage and frost resistance.The main contents and conclusions are as follows.(1)Referring to the European standard EFNARC and comparing with the results of domestic and foreign studies,the ECC with self-compacting performance is prepared as the matrix material.(2)The orthogonal test was designed to analyze the significant effects of dosage,particle size and vibrating time on the workability and mechanical properties of the mixture.Through range analysis and variance analysis,the influence degree of dosage on workability is greater than that of particle size,and only the dosage of wollastonite has a significant effect on compressive strength.(3)The effect of different dosage of 75μm wollastonite microfiber on workability of the mixture was studied by fluidity and V-shaped funnel test.The results show that with the increase of dosage,the fluidity of fresh mixture decreases and the outflow time of V-shaped funnel extends.When the dosage exceeds 30%,the mixture gradually loses its fluidity.(4)Compressive,flexural and direct tensile tests were selected to detect the mechanical properties of ECC with different dosage,and the bending toughness of ECC was investigated according to the toughness index method.The results showed that compared with the control group,the addition of wollastonite makes the 28 d flexural strength improve first and then reduce with the increase of the dosage,and the maximum flexural strength can be improved by 87%.The bending toughness has a slight lower trend,but it increases gradually when the dosage is less than 30%.(5)The influence of the dosage of 75μm wollastonite on the shrinkage and freezing resistance of the mixture was studied by shrinkage test and rapid freeze-thaw test.It is found that wollastonite microfiber can inhibit the shrinkage of the mixture well,and the shrinkage expression improved hyperbolic function can describe the relationship between dosage,age and shrinkage strain well.After 250 freeze-thaw cycles,ECC mixture with higher microfiber content still has better integrity and higher flexural strength.